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Planetary News: Space Missions (2011)Mars Exploration Rovers Update:Opportunity Closes in on Endeavour as Team Bids Farewell to SpiritBy A.J.S. Rayl
Opportunity seemed to sail with the wind behind her back toward the western rim of Endeavour Crater this month as the Mars Exploration Rover team shifted gears in preparation for a whole new adventure, taking time out only to bid a final farewell both privately and publicly to Spirit. Endeavour is estimated to be about 22 kilometers (14 miles) in diameter, and its western rim exposes outcrops that harbor clues of environments older than any Opportunity has found to date, promising to take the rover and the MER science team farther back in Martian time than any other site this rover has toured … back to that time, billions and billions of years ago, when Mars was warm and wet and rich with habitats from which life could emerge and thrive. It's been a long time coming. Ever since Opportunity pulled away from Victoria Crater in late September 2008, Steve Squyres, of Cornell University, the principal investigator for rover science, has repeated the rover's simple prime directive like a mantra: Drive, drive, drive. Opportunity has obliged and in July seemed to pull out all the stops, driving backward as fast as possible and putting nearly a mile in the rear view mirror to begin closing in on the much-anticipated destination. "We're almost there," Squyres marveled during a recent interview. "We are close enough to smell it."
When the rover first set out on the long journey, Endeavour seemed so far away. "We had such a long way to go and we realized our chances of getting to this crater were maybe not all that good," Squyres recalled. Mars is notorious and could have taken the rover out, as it threatened to do with a global dust storm in 2007. Then there is the reality of the rover, a robot field geologist comprised of nuts and bolts, carbon composites, titanium, and aluminum, along with the fact that the 7.5 year overland expedition has taken its tolls. Yet, Opportunity continues to rove on, without it seems too many cares in the world. "Opportunity has an arthritic shoulder joint on her robotic arm and is a little lame in the right front wheel, but she is otherwise doing remarkably well after seven and a half years on Mars," confirmed Bill Nelson, chief of the rover engineering team at JPL. So well that there are a good number of team members especially on the engineering side who are certain this rover has miles – and years – to go before she sleeps. "They will do a lot more than we give them credit for," assured John Wright, one of the MER rover planners.
After driving Thursday and Friday though, Opportunity took a breather this weekend, with less than 325 meters (0.20 mile) to go to reach the location where it will make “first landfall” at the humongous hole in the ground. If the “good girl” rover keeps the pace, sometime within the next week and a half she will be pulling into the southern tip of Cape York at Endeavour, at Spirit Point. Named in homage to Opportunity's twin, Spirit Point will be the rover’s gateway to the Noachian crust, geologic remnants from an early period on the planet characterized by high rates of impacts, erosion, valley formation, volcanic activity, and weathering of surface rocks that would have likely produced abundant phyllosilicates, processes that suggest a wetter global climate with warm conditions at least part of the time. Tucked away in some of that Noachian crust the team hopes Opportunity will find some of those phyllosilicates, specifically iron-magnesium smectite clays, a family of clay minerals that form in water, and which were detected last year by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) onboard the Mars Reconnaissance Orbiter (MRO). If Opportunity can uncover phyllosilicates, which were detected orbitally in the crater rim at Cape York, then it likely will have found the best evidence yet that water once pooled and/or flowed on Mars, in what was a warmer, wetter environment that could have been a past habitat suitable for life, complete with pH neutral water. Uncovering phyllosilicates would add another ‘first’ to the MER’s long list of achievements, and at the same time win what is something of a race with the Mars Science Laboratory rover Curiosity, which was given the objective of finding the same mineralogical evidence. As it appears now, Opportunity is poised to make the finding even before the bigger, faster, newer rover even gets off the ground in November.
Thus, the primo target at Endeavour – and what really has the scientists pressed up against the rover's windshield, metaphorically speaking – is the smectite at Cape York, and of course the chance to chalk up another big find. By all accounts the MER mission has been consistently scientifically gripping. But roving onto Noachian crust will be huge and the excitement factor is high and rising. "It's really getting high," confirmed Squyres. "Everybody's very charged up.” Including the rover, it seems. The only pause came during an interlude mid-month to say a collective 'good-bye' and 'thank you' to their other robot teammate Spirit, who stopped communicating in March 2010. Although the team tried for more than a year to rouse the rover after it went into low-power fault or 'hibernation,' Spirit apparently did not survive its fourth Martian winter and the rover's mission was declared over in May of this year. MER scientists and engineers gathered at Caltech's Athenaeum for a private team dinner, and a night of reminiscing. Up on Mars, Opportunity raced on, covering some 124 meters before calling it a sol. Then, the net day, on July 19th, an official "celebration" was held at JPL, where team members gathered again, a few hundred of the 4000 individuals who contributed to the mission taking part in a program that reviewed Spirit's achievements in words, pictures, and videos, and on that sol, Opportunity stopped too. Not surprisingly, Spirit shined, for better and even sometimes for worse, in the storytelling – of how she went silent after just 18 Martian days … how she climbed a mountain … went in search of a lake but found a volcanic environment that rewrote the science texts … how she found near pure silica, a sure sign of water, and a potential habitat for life … and the subsequent realization that she had also found carbonates indicative of a more neutral pH water … how she carried on after breaking her right front wheel and survived "rover-killing" dust storms. Yet, in the one-hour allotted for the memorial, there was just no way to adequately cover all that Spirit achieved in the name of exploration.
Like all great stories, the 2210+ Martian sols that Spirit worked on Mars were marked by the highest of highs and some of the mission's lowest lows, and always at the heart of this tale was a little rover that could. While the robot field geologist MER-A is now a carbon composite memorial to planetary exploration parked ostensibly forever in Gusev Crater, Spirit's story is not over. Not yet. There is at least a decade's worth of science to be analyzed and a generation of kids who grew up not knowing a world without Spirit on Mars. Meanwhile, the MER mission roves ever onward with Opportunity. The plains of Meridiani are visibly giving way to rocky, mountainous slopes and hills now, and a whole new backdrop of breathtaking scenery is coming alive in the picture postcards Opportunity is sending home. The drivers have been brushing up on the mountaineering techniques developed for Spirit's hike up Husband Hill back in 2004-'05, and considering other potentialities for the rockier terrain at Endeavour.
"It's going to be interesting driving, and we get to look at new stuff,” said rover planner John Wright, who’s been with the mission since before launch. Despite the experience gained from Spirit's pioneering ascent, the Endeavour rim is a new place altogether. “We're seeing slopes there that might be as high as 30 degrees, so we really need to scout it out before we drive up," Wright said. "We need to take a lot of images and carefully plan what we're going to do." The science team, meanwhile, is plotting Opportunity’s first science campaign. "The closest landfall to us where we can get the instrument deployment device (IDD) [or robotic arm of instruments] for the first time onto Merdiani Noachian is Cape York at Spirit Point, and that's where we're going," said Squyres. "Once we've gotten to Endeavour, the plan is to really look at it and eventually work our way south, but that will take plenty of time. It makes sense, scientifically speaking, to go for the jugular as soon as we can. We have no hint that anything is wrong, no hint that the vehicle is going to be anything but healthy for a long time to come, but we can't bet on that, and we're not gonna. The really ancient crustal material that's preserved at Endeavour's rim is priority number one.” If everything goes as planned, Opportunity should begin the new science campaign sometime in mid-August, more than seven and a half years after bouncing down on Mars and scoring the world's first interplanetary, 300-million-mile hole-in-one. "We're not there yet," cautioned Squyres. "But if we can actually get up on this thing, it's going to be like a whole landing site." Celebrating Spirit from California, EarthThe MER science team members gathered at JPL, where the rovers were born and are being managed, for its annual meeting in mid-July. On their agenda was a farewell to Spirit. On July 18, with the MER engineers, they held a private "wake," as Squyres first called it, at Caltech's Athenaeum, the private university club where discoveries and special events are often celebrated – and where Albert Einstein lived during his appointment as a visiting professor to Caltech in 1932 and 1933. [He first spent time at Caltech the year before, when he was working on updating his Theory of General Relativity.]
"The team showed up and we had dinner and drank beer, told lies, and just had a good time," Squyres shared with a chuckle. "A lot of stories that couldn't be told at the time were told last night. We needed a chance to kind of all get together face-to-face and give Spirit a proper send-off. That's what [the] night was about." The following day, Tuesday, July 19th, the NASA center held an official Spirit memorial and celebration in JPL's Flight Projects Center. Every one of the 426 seats in the auditorium was filled before the event began, and about as many JPL'ers were turned away, according to the center's public affairs office, left to watch the live NASA telecast from their offices. Familiar faces were everywhere … and everyone seemed to be smiling. Many members of the original team, including Pete Theisginer, manager of the Mars Exploration Rover Project through development and landing, Jim Erickson, the original MER project manager, who took a break from his new post at the Deep Space Network, and Jake Matijevic, a member of the original MER design team and former chief of the rover engineering team, among them. And at least one of the Student Astronauts hosted by The Planetary Society during the early days of the mission was in the audience, Abby Fraeman, now a grad student at Washington University, St Louis, working under the direction of Ray Arvidson, the deputy principal investigator for rover science.
John Callas, MER’s current project manager, emceed the event, recounting Spirit’s achievements and remembering rover moments as he introduced the speakers, panels, and film clips throughout the hour-long memorial. The reminiscing began at a critical point in the beginning, when it began for the public – landing night, January 3rd or 4th, 2004 depending on where in the world you were. “It was a very tense time, not only because it was challenging, but also NASA was going through a very tough time then too,” remembered JPL Director Charles I. Elachi. “When you look at the videos, you can see it in the faces of all the people as we were waiting for those signals moments before landing.” En route, Spirit had survived the largest solar storm on record. Then, in the hours before her slated landing, a dust storm was mucking up the entry, descent and landing team's parameters. But adjustments made, Spirit hit the Martian atmosphere right on time at 8:29 pm, Pacific Standard Time (PST), traveling at 12,175 miles per hour, 25 times the speed of sound. The entry went like clockwork. It began decelerating as expected, and at 25,000 feet, 446 miles per hour, the parachute deployed near the expected time and six minutes later it 'beeped' home that it had touched down and was bouncing. The spacecraft still had to stop. After what was for some an excruciating 16 minutes later, Spirit phoned home. She had landed upright and was ready to roll. The world cheered too that night and in that instant, JPL was the center of the Earth universe. Within 72 hours more than one billion people jammed the NASA and JPL and mirror websites to checkout the first picture postcards returned by Spirit and a robot hero was born. “Spirit lifted the spirit of NASA when it really mattered,” summed up Elachi. “That [landing] created such excitement,” he said to the team members, “and you believed in NASA and what NASA can achieve, the things that are always 'impossible.'”
It hadn’t come easy. Spirit was, as Elachi had recalled "not an easy-going rover." In fact, her personality began to form even before the mission launched and from the outset it was becoming apparent that this rover could be trouble. “Spirit was the problem child of the development, like your first born, always in the cookie jar first,” recalled Theisinger, who led the panel of engineers that took the spotlight to highlight some of the important moments and happenings during the rovers’ pre-history or early development. So many ideas are input, so many decisions are made, so many little things changed that it would be impossible to review Spirit's creation in entirety during the ceremony, but Theisinger's panel did touch on a few of the critical 'hits,' at least one of which helped prevent a potentially catastrophic 'miss.' One of the distinctive features of Spirit and her twin is the solar array formation, which gave the robots "winglets" and their now so familiar appearance. Kobie Boykins, the solar array mechanisms and structures cognizant engineer, was charged with, among other things trying to figure out how to get the rovers’ solar arrays to fold up and inside the tetrahedron-shaped shell for the ride to Mars. “It had to produce 950 watt hours and it had to fold into a tetrahedron,” Boykins said. “We were limited on inside by the canister that held parachute and limited outside by the lander – and then our illustrious PI, Steve Squyres, saying, 'Can you get just a couple more cells?'" Once all the objectives were met, weight became an issue. The rovers were 2 kilograms too heavy. Their solar “winglets” were put on chopping block. The original analysis indicated that even without the winglets, the rover would have enough power capability to survive 90 days. “Then Kobie and his contractor cohorts came back with a new power analysis that indicated with the winglets off, we were really in trouble,” remembered Theisinger. “Steve was really depressed for about 20 seconds before he realized – that means we're going to have to put the winglets back on.” It's almost impossivble now to imagine the rovers, icons that they have become, without their "winglets."
Boykins, also a member of the ATLO (Assembly Test and Launch Operations) recalled Spirit’s antics at the Cape, after being buttoned up for launch. “The bad sister,” as he described MER-A, essentially 'spit' out a screw from the Pancam mast assembly (PMA). “That was just the beginning of Spirit’s fun,” he said. No sooner had they figured out a workaround when a single point ground issue caused them to have to open up the rover’s tetrahedron shell, something done only in an emergency. They managed to straighten the rover out, replacing an electronics card and adjusting the PMA,and get her buttoned back up for launch in time for the planned window. After succeeding in getting the attention she apparently wanted, Spirit was finally ready to go. “Later in the development, we began to worry about winds,” Theisinger said, continuing the story. “It occurred to us maybe we ought to find a way to cancel the wind down and so DIMES [Descent Image Motion Estimation System] was developed." Jeff Mellstrom, who led the DIMES effort piked up the story. “It was late 2001 people began recognizing some of the risk associated with winds,” he recalled. Comprised of a descent camera and an algorithm for estimating horizontal velocity using image, inertial, and altitude measurements, DIMES became the first autonomous machine vision system used to safely land a robotics payload on another planet. It was, in effect, a kind of insurance policy. DIMES not only performed successfully, but without it Spirit might not have made it. During the rover's landing in Gusev Crater, the landing system used the measurement DIMES provided to remove a possibly catastrophic horizontal velocity. “For Spirit, it was an insurance policy that paid off,” concluded Mellstrom.
Getting the lander to the surface, however, was only “the first part of the puzzle,” Theisinger continued. “Getting the rover off the lander and [all] six wheels on the ground in order to do science was the next.” Daniel Limonadi, one of the engineers responsible for impact to egress, explained the “last foot of landing,” as he called it. “When [Ed Weiler, Associate Administrator for the Science Mission Directorate, at NASA HQ] and company approved this mission, nobody thought the last foot would take on the order of 10-12 days to accomplish on Mars, but we didn't consider the rover landed until all 6 wheels were on the ground,” he explained. The impact-to-egress team’s immediate tasks were to see Spirit through the stop, retraction of the landing airbags, opening of the lander petals and the solar arrays, and getting the rover to a power safe state. Then, they commanded the rover to deploy the Pancam mast assembly and take its first pictures with the panoramic cameras. As those images came in to JPL that night, the scientists were ecstatic, some "in a state of shock and awe," as Jim Bell, Pancam lead, of Arizona State University (ASU) and president of The Planetary Society, described it. The impact-to-egress team members though were biting their nails, seeing that one airbag didn't quite go where it was supposed to go, and it was right in the rover's exit path. While a few members of the team addressed that issue, Limonadi and others carried on to the next step in the process: getting the vehicle up and ready to rove. Once Spirit stood up, the “signature” they were looking for “was missing something that day,” said Limonadi. A latch that should have locked in place didn’t quite look right. “After deliberating for a night and thinking about it, we redid that move, confirmed [the latch] was in place and moved on." By then, a workaround the airbag was defined, Spirit. "We spent a few sols dancing around the lander to avoid the front exit path that was blocked, and turned around and drove off the other side," Limonadi recounted.
“There's a lot we didn't talk about – the impact of a short schedule and it's impact on everyone's nerves… the parachute issues … meeting with Ed [Weiler] and Charles [Elachi] in the last few days before launch to convince them we really were safe to go … the Sol 18 anomaly,” Theisinger acknowledged. “Or the great grandmother of all solar storms … or the dust storms of Mars." In that moment of Theisinger condensing more than six years of exploration and adventure, it became abundantly clear just how much Spirit had gone through since landing – all of which led to one stellar mission. “Spirit's discoveries have changed our understanding of the Red Planet,” said Callas segueing into Spirit’s scientific efforts. “We know now that Mars was not always a cold, dry and barren planet. That at one time liquid water flowed on it surface, sustained by a thicker atmosphere and warmer temperatures. At least, kilometer-scale lakes persisted in places. And that there were even sources of energy, hydrothermal systems, that could have supported life in this earlier habitable world.” Following a video review of Spirit’s major discoveries, Callas introduced “the ever essential Dr. Steve Squyres,” who led the panel of scientists, which included Oded Aharonson of JPL, Steve Ruff of ASU, and Dick Morris, of NASA’s Johnson Space Center, each of whom drove Spirit’s data to important scientific findings. "The last panel did a terrific job of giving you a sense of what an adventure it was to get Spirit from initial concept to the surface of Mars – three and a half years of terror and tension," Squyres began. "That three and a half year adventure was then followed by another six-year adventure of scientific discovery on the Martian surface, and what we're going to try and do in the next minutes here is share some of that scientific adventure with you.
Squyres began the review of Spirit's "scientific adventure" telling the stories that accompany a few of his favorite images. Behind the panel and at the front of the stepped auditorium, an image of Spirit at the rock Adirondack is projected onto a movie screen. Of the some 124,00 pictures that Spirit sent home however, "this is my absolute favorite," said Squyres. For those not intimately familiar with the mission, it would seem an odd choice. It's not one of the lush Pancam color panoramas of a Martian vista that takes your breath away, but rather is a black and white image taken by the rover with her front hazard camera, rather mundane by most everyone's measure. But for Squyres this image represents far more than a picture. “Eighteen days into Spirit's mission we appeared to have lost the vehicle," he remembered. "She just went silent. And we didn't know what was going on. It was absolutely terrifying. We were up, not sleeping for three days straight. It turns out Spirit was as well." [Spirit's flash memory had been overloaded and the rover was in a continuous reboot loop.] After the laughter subsided, Squyres continued. "It was because of a software problem. The team did a brilliant job of analyzing what was going on, solving the problem, getting control of the vehicle. And this was the first picture that came down after the anomaly, showing us that we had a healthy vehicle ready to start exploring on the surface of Mars."
While Opportunity was the lucky rover that made most of her "critical discoveries" in the first 60 days after landing, "Spirit's real mission of scientific discovery began when [the rover] headed down from the summit of Husband Hill into the terrain there,” he describing the panorama dubbed the “Mt Everest Pan," which the rover took at the summit of Husband Hill about 600 days into the mission. It shows the view to the south "and what turned out to be for Spirit the geologic promised land," as Squyres described it, where Spirit would groundtruth the first hard evidence of carbonates on Mars, and out in the valley would discover a real Martian silica valley, something that surprised the scientists and rewrote the science texts to show that Gusev was not a former lake but an explosive, volcanic environment. Aharonson picked up the story of Spirit's scientific adventure by talking about Home Plate, the circular approximately 80-meter diameter plateau that the rover spent several thousand sols studying. Using lush images that Spirit took with her stereo panorama cameras, he described the layered rock at the top and coarsely layered rock at the bottom … a rock that was a bomb sag … and the interpretation that is “fairly widely accepted now that this was a big volcanic eruption, a pyroclastic eruption that deposited these layers on top of one another.” It’s possible, he continued that “the eruption happened at the center of Home Plate and the sediment just felt on top of the hole”. Or, another possibility is that it happened somewhere else and the sediments just got capture in Home Plate. Either way, this was probably a very violent eruption,” he said.
“One of the things they did, Aharonson said, was "to carefully look at the geometry of these layers on this side of Home Plate." By tracing the layers, they discovered each sloped down toward the center of Home Plate, and when Spirit drove around to the other side she found those layers also dipped toward the center of the formation. Spirit's investigations at Home Plate present an alien example of physical vulcanology, "one example where we really understand how this process happens on another planet." Since "pyroclastic eruption is one of the hypothesis we have for all the rocks we see on the other side of the planet with Opportunity," Aharonson added, "having a sort of the archtypical of pyroclastic event on Mars" is "very useful" to the planetary science world. Another clue for us all that Gusev was anything but a lake came when Spirit "turned lemons into lemonade," as Steve Ruff, of ASU, the downlink lead for the miniature thermal emission spectrometer (Mini-TES), put it. “Home Plate was our best, last hope for evidence of lake sediments," he explained. "We were both excited and disappointed to discover it was a story of interest to vulcanologist,” he said to laughter.
As Ruff showed an image in which “a very ratty little outcrop of rock," about 6 inches high and 18 inches wide, appeared. “This was our first clue we were onto something interesting at Home Plate,” he said. Spirit had churned up some light toned soil as she dragged her lame right front wheel. "Our Mini-TES looked at this and through very dirty, dusty mirrors – by this point in mission that instrument was contaminated with dust [courtesy the global dust storm in 2007] but I could just make out the features spectrally of what looked like silica. It turned out it was. And before Spirit’s investigation of the area was over, the rover, by having to drag its bad right front wheel had churned up a sample of near pure opaline silica in what Squyres previously has described as "Mini-TES' finest hour." “This is a place covered in lava flows and to find something high in silica is totally opposite of what we expect in a lava-rich place," Ruff explained. Opaline silica is a mineral that forms in environment on Earth that are highly thermal. "This is one of the holy grails of Mars exploration – finding places on Mars where hot water is interacting with rock," Ruff continued. "That's because on Earth, these are places where microbes like to live. Microbial life rose on the side of hot springs, and it rose on the edge of fumaroles and steam vents and the beauty of opaline silica is that it actually can entomb those same microbes. So this is a place on Mars that could have had life, [was once] a habitable environment, and it could have even preserved that microbial life in silica for us to maybe go back in the future and collect.” While the lake story at Gusev faded, a new story of hydrothermal alteration and different kinds of potentially habitable environments emerged. The persistence and dedicated research of a self-professed “crudologist," Dick Morris, senior planetary scientist and manager of the Spectroscopy and Magnetics Laboratory down on Earth at JSC, advanced the scientific adventure.
For hundreds of year, Earthlings have stared at Mars and wondered about what appear to be river channels that cut through its various rusty red landscapes. “One way to get these river channels is to have had water running along time ago on ancient Mars, and one way to do that is have a warm Mars and a very thick CO2 atmosphere so it rains a lot," Morris said. "Then we have a lot of water and CO2, and from that you can get carbonate." That notion has been around since the 1980s, but it was never resolved because no spacecraft or scientific instrument had been able to detect any of this carbonate that should have been there. “Well Spirit had a lot to say about all this," Morris said. As Spirit hiked down Husband Hill, she stopped near the bottom to snuggle up to an intriguing looking outcrop dubbed Comanche, nestled in a carbonate rich area. Finding and proving that took time and perseverance and the willingness to follow a hunch.“We came by this outcrop in 2005, and we published a paper in 2010," recounted Morris. "It took five years to figure out what was going on here. Part of the reason was we had to do some homework. One thing was that Mini-TES had to get the dust out … and we had to go back to laboratory and look at the Mössbauer data again … plus APXS provided chemistry, and the amount of carbonate," he pointed out. “We put that all together and did the calculations and there was between 16 and 34% -- that is a lot of carbonate. Time will tell if this was a part of the warm and wet early Mars," Morris concluded, as he turned the program back to Squyres. “When you get to the end of something like Spirit's mission, you find yourself asking questions about – what's our legacy?” Squyres said, beginning his wrap-up. “Mars today is a cold and dry and desolate world, but Spirit's discoveries have helped show us that in the past it was a very different place. At Gusev Crater in the Columbia Hills, it was hot. It was violent. There were explosions, steam vents and hot springs, and ecological niches that would be capable of supporting some of the hardy sorts of microorganisms you can find in extreme environments on Earth today. So I think the scientific legacy – while it will continue to grow as we continue to analyze the data – is clear. But there's a human dimension to the legacy as well,” he reflected, acknowledging that the mission didn't turn out the way he expected it would.
"What was initially conceived as a fairly simple geologic experiment ultimately turned into humanity's first great expedition of exploration across the surface of another planet. When you think about the way the great historic voyages of exploration have typically played out in the past – they would get in their ships and sail off over the horizon – and 2, 3 or 4 years later they would come back – or they wouldn't – and the ones who came back would have stories to tell. But we have been able to tell the story day-by-day, sol-by-sol, as it happened and share that with literally everyone in the world who wanted to follow along." Offering the world an E-ticket to follow along brought untold renown to the mission, and to NASA, and people everywhere around the world have followed the adventures of the robot field geologists from the beginning. “We know this story has captivated and caught the imagination of many people,” Squyres continued. “These rovers were built in part by older people like me who grew up in the Sixties watching Mercury, Gemini, and Apollo on television, and dreaming of sending spaceships to Mars someday. And then we got to do that," he said. "My fondest hope for the legacy of Spirit is that somewhere there are young people, kids who watched the Spirit landing on television and saw us all jumping up and down and thought – this is unbelievable – and who heard about the scientific discoveries and the hot springs on Mars and looked at that and said to themselves: 'That's pretty cool. But I bet I can do better.’ If that is part of our legacy, I think that's one of the best things we could leave behind.” Although Squyres is never easy to follow, Callas met the challenge and eloquently brought the memorial to an end, nodding subtly to the Spirit that will forever live still in the hearts and minds of the team members and anyone who ever cared about the rovers. “We can't do the impossible,” Callas said, addressing the untold emotions. “We can't make these machines operate forever. But we have come as close to that as humans possibly can. Spirit's very accomplished exploration of Mars has rewritten the textbooks about the planet. Further, this rover has changed our understanding of ourselves, our place in our Universe, and has approached the questions of 'Are we alone?' and 'What is the future of this world?' But beyond the exploration and scientific discoveries, Spirit has given us a great intangible. Mars is no longer this distant, alien unknown world. It is now our neighborhood and we go to work on Mars everyday,” he noted.
“Let's also remember that this great accomplishment did not come at the expense of vanquishing some foe or outscoring some opponent," Callas said in conclusion. "Spirit did this – we did this – to explore, to discover, to learn for the benefit all humankind, and in that respect, these rovers are the highest aspiration of our species. Well done little rover. Sleep in peace. Congratulations to you all. And thank you all very much.” It was a fitting tribute and could have easily gone on another hour or two. [You can catch a replay of the NASA-TV broadcast here.] Coupled with the team’s wake the night before, Spirit finally got her proper send-off, and that seemed, for so many, essential. “I’m glad we did it,” Squyres would reflect later. Shortly after the event ended, a student at JPL for a summer internship approached Squyres. "Watching the rovers and following them were an inspiration for me –" she began. And, as she continued, it was obvious that while Spirit may no longer be functioning, the rover’s legacy is very much alive. "That's was exactly what I was hoping for," Squyres told the MER Update recently. "This mission has been in the literal sense of the phrase the adventure of a lifetime. I don't ever expect anything in my professional career to top this. Certainly nothing I did before this comes close – and it's not like I've had a really boring life. I got to work on Voyager with Carl Sagan. But Spirit and Opportunity – and working with this team – professionally, they are the best things that could ever happen to me." On so many levels, the Mars Exploration Rovers have been the best thing to happen to space exploration during the last decade. This little rover who could, did, roving into the scientific spotlight again and again, driving her way into the hearts of humans around the world with her first ‘beep,’ garnering NASA so many banner headlines that it's almost impossible to fathom that the Mars Program is threatened. But these are tough economic times for those who seek to explore new worlds and/or who would seek to enrich minds as opposed to personal bank balances.
NASA Associate Administrator Ed Weiler offered advice to all the current and future Mars explorers in the auditorium. “This should be a positive day,” he said. “Most importantly stick together. Don't get involved in negativity about budgets – Mars in and Mars out. This nation cannot afford not to continue the Mars program, especially with our President saying the ultimate destination for human spaceflight is Mars. We're the ones who are going to draw the maps and prepare the groundwork for those humans to get there. We have to continue the Mars Program. It's not for JPL, and not for NASA. It's for our country.” In the week and a half since, the team's attention has converged completely back onto Opportunity. "We have a rover on Mars that has an exciting adventure ahead of it that's probably the greatest since it landed," Callas pointed out, "and there's a lot to do. The best tribute we can give Spirit is to do the best we can for Opportunity." Opportunity from Meridiani PlanumOpportunity began the month of July taking care of business, which on Sol 2643 (July 1, 2011) included conducting a forward link ultra-high frequency (UHF) test with MRO, along with the usual picture taking, atmospheric observations, and systems checks.
With multi-sol planning for the 4th of July holiday weekend, the rover drove only twice during the first week of the July: on Sol 2645 (July 3, 2011) for 162.14 meters (531.95 feet or 0.10 mile) to the southeast; and on Sol 2649 (July 7, 2011), for 141.17 meters (463 feet) to the southeast. Power fluctuated throughout the month, as typical for this time of year, with levels bouncing from 420 to 417 and back up to 435 watt-hours. The atmospheric opacity, or Tau as the team calls it, has been between a hazy 0.94 and 1.03, with the rover's solar array dust factor moving around 0.574 to 0.596. Although the rover could stand another dust-clearing, Opportunity has plenty of energy to drive, and enough buffer so that as the second week of August took hold, she was able to wake up very early on Sol 2650 (July 8, 2011) to uplink data via an ultra-high frequency (UHF) relay pass to return to Earth. The rover has been conducting both commanded and blind drives to extend her drive distances and put as much possible distance behind her. The commanded drives, however, generate a lot of picture data that tends to back up onboard and so the rover has been taking every chance to downlink as much data as possible.
On Sol 2651 (July 9, 2011), Opportunity took another atmospheric argon measurement with the alpha particle X-ray spectrometer (APXS), part of an ongoing, mission-long experiment. Also on that sol, the rover conducted a test that involved warming her electronics and staying awake longer to mitigate clock drift. “The rover has accumulated large amount of clock drift, so the spacecraft doesn't know the right time,” reported Nelson. “The clock is running slow. This causes some problems." The clock drift error creates "mis-estimates" of the rover attitude in the east-west plain, he explained, though it doesn't do much in north-south plain. "If I warm up the clock I can actually reverse the amount of clock drift and start catching up on clock drift." That was the theory underling the test. "It worked, but not well enough or fast enough," reported Nelson, "and it adds a lot of complication.” On Sol 2652 (July 10, 2011) Opportunity drove 150.93 meters (495.17 feet), continuing in the southeast direction towards Spirit Point, located at the southern tip of Cape York on the rim of Endeavour. Then two sols later, the rover drove another 80.36 meters (263.64 feet) blind – in order to avoid too many data generating products – to the southeast. During that drive, the rover crossed another milestone, 32-kilometers or nearly 20-miles on the surface of Mars. Opportunity continued to make "very good progress," Callas noted, as the month wore on. In fact, the rover drove five times during the third week of July, logging more than 510 meters of drive distance. On Sol 2656 (July 14, 2011), Opportunity roved for 80.35 meters, then conducted another atmospheric argon measurement with the APXS. Three sols after that, on Sol 2658 (July 17, 2011), she completed a drive of 124.17 meters (407.38 feet). That jaunt took her past the 20-mile mark (32.2 kilometers), more than 50 times the mission's original distance goal.
That drive also included an autonomous hazard detection portion during which Opportunity paused at intervals to check for obstacles before proceeding. "Autonomous hazard detection has added a significant portion of the driving distance over the past few months," said Alfonso Herrera, a rover mission manager at JPL, who has worked on the rover missions since before launch in 2003. "It lets us squeeze 10 to 15 percent more distance into each drive." Following a Martian day of rest, Opportunity headed on, logging 119.51 meters (392.09 feet) on Sol 2660 (July 19, 2011), 130.59-meters (428.44-feet) rove the next sol, and on Sol 2662 (July 21,2011), she put another 55.63 meters 182.51 feet) behind her. After the Sol 2662 drive, Opportunity finished her day of work conducting a visual odometry experiment, to measure the precision in which she can determine her relative position, something that will benefit future radio tracking experiments. But as the final week of July set in, the rover kept the pedal to the metal, and set out to make another long drive of 145.09 meters (476.01 feet) on Sol 2664 (July 22, 2011). That plan ended prematurely, however, when flight software detected problem in shoulder joint. "It thought it had become unstowed," reported Nelson. "It hasn't recurred, and there's not a lot to say yet. We've got to get some data to really crunch here." Despite all her hard driving and record distances, Opportunity's right-front wheel currents, which have been of significant concern for more than a year now, remained "behaved." The rover continues to drive backwards and warm its right front wheel actuator to mitigate the slightly elevated currents. "The right front wheel current continues to be a concern, but a combination of heating and backwards driving has kept it in check,” Nelson said. On Sol 2667 (July 25, 2011). Opportunity drove 84.38 meters (276.83 feet) toward a bedrock target that would be the last the rover will sample between Victoria and Endeavour craters. The following sol rover drove on toward Endeavour, ripping another 122.10 meters (400.59 feet) up to the bedrock. Immediately noticeable were the blueberries sprinkled all over the sampling target. The rover deployed her the IDD on Sol 2669 (July 27, 2011), quickly inspected the outcrop, then took off again, driving 63.61 meters (208.69 feet) on her Sol 2670 (July 28, 2011).
During that drive last Thursday, Opportunity cruised past the 33-kilometer mark, but she didn't hang around celebrating. The very next sol in fact, the rover put another 69.20 meters (227.03 feet) behind her, ending the month of July 2011 with her odometer at of 33,106.25 meters (33.10 kilometers or 20.56 miles). "We've been making excellent progress," said Callas during a recent interview. "It wasn't that long ago we said December or later. The terrain has been very cooperative and we have been free of anomalies or complexities that might have slowed us down. Once we get to Endeavour the pace is going to slow down, because we're going to do in situ science investigations there." Once Opportunity pulls into Spirit Point, the rover's first assignment, said Squyres, is to check out the Noachian crust preserved in the rim of Endeavour. "Our plan is to head to the southern tip of Cape York, which is a place we've named Spirit Point, to drive essentially as quickly as we can up onto the eastward facing slopes at this southern end," Squyres confirmed. "That's where it looks like the ancient Noachian terrain is best preserved," he said. "You have to be a little careful about trying to plan these things too much," he cautioned. "If you over-plan you can become a little too attached to your plan and then when you get there and you are confronted with the reality and it's different than what you expected, you have to be ready to change things. We're not even going to know what we're dealing with until we put in a RAT hole and really look at this carefully with the MI and the APXS. So I'm sure we'll jump to that pretty quickly, and then after that, we'll just see what we see."
And soon, we will see what they see. The rover has less than 325 meters (1066.27 feet) to go now. "But we're not there yet," Squyres reiterated. "Things can happen. It’s been a remarkable drive and a remarkable accomplishment to get this close, but we still have a little ways to go." You'd be hard-pressed at this point however to convince anyone, Squyres likely included, that Opportunity is not going to make it to Endeavour's rim and the rover drivers are just as excited as the scientists, in no small way because much of the driving on Opportunity for the past year has been – well, boring. Now, new obstacles will challenge their skills and they're ready. In addition to brushing up on Martian mountain driving by reviewing Spirit’s climb up Husband Hill way back in 2004-‘05, the rover planners are considering new techniques in preparation for Opportunity’s venture up into the rim of Endeavour. "Some of the people who have been around a long time and have moved back and forth between rovers have experience driving in the Columbia Hills,” said Wright, who lays claim to having driven the rover's longest backward drive 165.67 last month. “We're having those who haven't go back and plan a drive up a hill or through some interesting terrain Spirit went through, and then we go back and compare what they planned to what the people on shift that day actually planned." While the Spirit drivers are teaching other drivers the lessons learned from driving in the Columbia Hills with Spirit and there are valuable techniques to be learned, Endeavour is a whole new arena. Moreover, there are "some interesting differences" with the rovers, added Wright. "Spirit at the time [of hiking Husband Hill] was still going forward. The right front wheel was still moving. It was flaky at times. For a period of time there on Spirit, we would turn the that wheel off 90% of time and then on for 10%, so we would drag it for 90 centimeters and then drive for 10 centimeters. That way if it caught on a rock it would bump up and over it and then continue dragging it. With Opportunity we always want to drive backwards because of the currents in its right front wheel. But we also have more mobility because we have six wheels of thrust pushing us forward," he explained.
After spending the weekend, her Sols 2672 and 2673, conducting remote sensing and taking a breather, Opportunity will drive on. Although the rover is now in a period of limited driving because of the timing of commands and communiqués between Earth and Mars, there will be no stopping the team -- or Opportunity -- this coming week. The hopes are that the rover will be able to put in at least two drives before next weekend. And perhaps by the end of the drive after that, the rover will be at Spirit Point. "The scenery is starting to get really spectacular," said Squyres. "Everyday looks different now. Things are really changing as we get in close. Every downlink is exciting. We know we're going to get into some very different geology and we don't really know what it is. This is going to be exciting." |
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